English: The large, v-shaped Spencer Gulf sits on the southeast coast of Australia, opening to the waters of the Great Australian Bight. Surrounded by large coastal saltmarshes, mud flats, seagrass meadows and mangrove forest, Spencer Gulf provides important habitat for a wide range of species, some of which live only in this area. The ecosystems found in the Gulf also support a robust commercial fishery, providing about half of all the harvest for the state of South Australia, as well as thriving ecotourism and recreational industries. An area near Whyalla, in the northwest part of Spencer Gulf, is the only known place on Earth where the Giant Cuttlefish breed in large numbers.

The water in most estuaries is more saline near the ocean and, thanks to rivers and rainwater runoff, the near-shore waters are less saline. That’s not the case in Spencer Gulf. Known as an “inverse estuary”, the water is much more saline closer to land, becoming less saline as it approaches the ocean. The northern Gulf receives little inflow of fresh water, thanks to a dry, hot climate inland. The inland lakes are extremely saline, becoming crusted with white salt (or drying up completely) in the baking sun.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Aqua satellite acquired a true-color image of Spencer Gulf on August 14, 2019. The rich marshes, mangroves, and coastal area appear green from lush vegetation. Green quickly fades to orange and tans approaching the arid inland, where large salt-encrusted lakes punctuate the landscape. Colorful swirls of milky turquoise and teal swirl in the waters of Spencer Gulf and the smaller St. Vincent Gulf. These swirls are likely to be caused primarily by suspended sediment, but some color may also be from colonies of microscopic, plant-like organisms called phytoplankton.